The present invention relates to a method and apparatus for controlling plasmas enabling plasma processing with high quality by controlling parameters for plasmas such as an electron temperature and a density distribution of the plasmas.
A plasma processing apparatus for generating plasmas by introducing microwaves in parallel with a magnetic flux density into a processing chamber applied with a magnetic flux density to such an extent as to cause electron cyclotron resonance has been described in, for example, Japanese Patent Application Laid-Open No. 55-141729.
Plasma processing apparatus using microwaves under a magnetic field have been used generally in recent years since they can generate plasmas at high density even in a high vacuum region and correspond to processing conditions over a wide range. The electron cyclotron resonance phenomenon is utilized in most of such apparatus. The electron cyclotron resonance as discussed herein is a resonance phenomenon that occurs upon coincidence between the frequency of a cyclotron movement of electrons under a static magnetic field and the frequency of microwaves having a wavelength of about 1 cm to 30 cm and it is known that the electric power of the microwaves can be absorbed efficiently into plasmas upon occurrence of the resonance.
In a plasma processing apparatus using a static magnetic field, the density distribution of plasmas has been optimized by adjusting the distribution of the static magnetic field in order to attain uniform processing. However, in a plasma processing apparatus using the electron cyclotron resonance phenomenon, since a static magnetic field having a higher magnetic flux density as compared with usual plasma processing apparatus is used, there has been a problem that the size of an electromagnet for the control of distribution is also increased.
Since the degree of integration for LSI is increasing, it is necessary to make the quality for the plasma processing higher. In compliance with the trend, a technique for controlling the characteristics of plasmas is necessary. The inventors have considered the case of plasma CVD. For instance, in a case of forming a thin Si film by using monosilane as a reaction gas, it has been known that SiHm radicals (m=0-3) in monosilane plasmas play an important role for reactions. Although it is not apparent which radicals, among them, are most important for the film formation, it is considered that if certain radicals can be excited selectively, high quality thin films at high purity with less hydrogen atoms liable to be contained as an impurity in the films can be formed. Since each of the radicals have inherent excitation energy respectively, it is necessary to control an energy given from plasmas to reaction gases in order to form certain radicals selectively. In view of the above, it becomes necessary to control the energy of electrons (electron temperature) that give an energy by collision to the reaction gases. However, in existent plasma CVD apparatus, since the plasma parameters can not directly be controlled, control has been conducted only by the optimization for film forming conditions by adjusting process conditions such as a film-forming pressure or a plasma-confining static magnetic field.
The foregoing requirements are also applicable to a case of plasma etching. That is, for efficiently exciting active species that contribute most to the reactions, it is necessary to control parameters of plasmas such as the density and the electron temperature of plasmas. Further, in a case of bias sputtering film formation, it is known that the coverage ratio for steps and crystallinity of films vary depending on the amount and the energy of ions irradiated to a substrate to be processed during film formation. In a case of wiring films, the coverage ratio for steps and the crystallinity of films are important parameters that determine the life of wirings and it is necessary to control plasmas near the substrate to be processed In order to form wiring films with high quality.